Treatment options for rising damp

Chemical DPC treatments were introduced as an alternative to mechanical damp-proof courses such as lead plates and various bitumen compositions. The chemical compounds used to try and create an impermeable barrier to damp are classed according to the way they act on masonry pores. Some chemicals fill pores in masonry, obstructing them and therefore prevent water from rising while others make the pores water repellent, modifying the surface tension between the pore surface and the water which makes the contact angle greater that 90o so that the resulting tension causes a downward pressure which prevents water from rising (i.e.inverts the meniscus that you can see in test tubes etc.)
The pore filling compounds include silicates and acryl amide gels. Silicates ( like Na2SiO3 or K2SiO3 ) are injected in a strong alkaline solution. The products of the reaction are silica gel (SiO2 + nH2O ) which is intended to fill the pores, together with some damaging salts ( sodium carbonate and potassium carbonate )The waterproofing/repellent compounds include silicon resins ( silanes and siloxanes), siliconates ( in combination with silicates) and silicon micro-emulsion.
However there is a serious drawback which is common to all chemical damp-proofing treatments in that they do not provide an absolute barrier against rising damp but instead they form a ‘diffuse band’ which only ‘controls’ the rising damp without stopping it. When fluids are injected into a heterogeneous such as brick or mortar they do not totally fill up the porous structure neither do they completely push out the water in front of the advancing injected fluid. Instead, the fluid tends to finger within the substrate, a process known as viscous fingering. Fingers of the injected material form when the fluid takes the path of least resistance such as larger pores or cracks in the brickwork. These pathways are not the most important elements in the conductance of water up the wall as this tends to be via finer pores. When injecting into a damp wall the fingering is increased, especially with solvent based systems, as these are not miscible with resident damp- which often makes the whole practice of injecting a damp wall pointless.
Despite this injection is still the most popular system of installing a damp-proof course and are usually offered by damp-proofing contractors whose installation is covered under British Standard (BS 6576:2005- Code of practice for diagnosis of rising damp in walls of buildings and installation of chemical damp-proof courses) and usually comes with approval through a British Board of Agrément Certificate BBA (example- Agrément Certificate 95/3210 for Triject Chemical Damp-proofing system issued to Triton Chemicals).
Holes are drilled into the thickness of the wall to attempt to saturate a zone usually around 75-150mm high at approximately 150mm above the external ground level at various centres and depths. A damp-proofing fluid, usually based on silicons or aluminium stearates, is then pressure injected into the wall. For a brick to be an effective damp-proof barrier it needs to be injected for approximately 20 minutes and therefore to treat an average sized house effectively it would take at least two days and as most injecting jobs are finished in around 3 or 4 hours then there is unlikely to be any proper water-proofing effect from the damp-proofing fluid. For more information on injection times please refer to an article by I'Anson S J & Hoff W D (1990) Chemical Injection Remedial Treatment for Rising Damp - II Calculation of Injection Times. Building and Environment Vol 25 No1 pp 63-70.
This system usually relies on a dense sand/cement waterproof plaster to hold back any dampness in the walls as most treatment companies can never be certain that the brickwork being injected under pressure is totally saturated as this leads to viscous fingering whereby the damp-proofing fluid follows the line of least resistance leading to an ineffective chemical damp-proof course. The specification of the plaster is usually a dense sand/cement render which itself will prevent the passage of moisture onto internal wall surfaces.
Full treatment to an average sized house can easily exceed £5,000 and it is not just the expense to worry about but there is usually a lot of disruption internally with the removal of wallcoverings, skirtings etc and then all the hassle of re-decorating after allowing the walls to dry out.
In many cases damp-proofing works are only undertaken as a part of a mortgage condition to obtain a guarantee against the recurrence of rising damp.
A more recent innovation in the injected damp course market is the use of gels and creams which are squeezed into pre-drilled holes using a large mastic gun. These materials have only been used for the last 5 years or so and there is no evidence to indicate whether they are effective or otherwise but somehow it does not seem likely that they will be as effective as broken down physical slate or bitumen damp courses that they are intended to supersede. They are touted as a quick and easy way of inserting a damp-proof course but in practice these materials are hard to use leaving globs of cream or gel oozing out of the holes and they often don’t diffuse into the brickwork in high humidity levels ( i.e. when the wall is wet) and even after 2 or 3 months the gel or cream may still not have penetrated into the brickwork which reduce their damp-proofing effect.
The active components of a damp-proofing cream can only react and become effective when the micelles of the emulsion of the cream break and the product becomes liquid. Results of tests indicate the micelles (which contain the active damp-proofing ingredients) cannot break in the presence of water and as these creams are intended to be used as damp-proofing barrier in damp walls then this form of damp-proofing is ineffective in damp walls.
This peer reviewed paper entitled ‘Evaluation of Spreading and Effectiveness of Injection Products against Rising Damp in Mortar/Brick Combinations’ concludes that ‘with respect to the spreading and effectiveness of cream products, it can be concluded that in 100% saturated substrates no spreading can take place because the products does not become liquid, while in dry substrates, the spreading is limited’. Basically what it is saying that damp-proofing creams remain as a cream in damp walls and therefore do not work and also that even in dry walls the spread into the brickwork is limited to a few centimetres.
Safeguard Chemicals have now introduced and new form of damp-proofing called DryRod which is, according to Safeguard, so effective that in most cases waterproof plastering is not required. In the past, waterproof plastering systems served a dual purpose of backing up the damp-proofing system’s performance and controlling hygroscopic salts. Safeguard state that the DryRod damp-proofing system does not require back-up from a waterproof plastering system but perhaps what they ,other damp-proofing manufacturers and damp-proof course installers mean is that previous damp-proofing systems were ineffective and relied on the waterproof plastering to prevent rising dampness from recurring.
Prior to opting for silane diffusion via cream injection Peter Cox had a transfusion system of installing a chemical damp-proof course whereby the siliconate damp-proofing fluid was gravity-fed through bottles and tubes placed in drill holes. The damp-proofing fluid would then diffuse slowly into the wall and saturate the brickwork filling voids and pores whilst avoiding the viscous fingering which occurs with pressure injected damp-proof systems. Currently there is only one transfusion damp-proofing system available in the UK and this is a frozen damp-proof course known as Freezteq whereby frozen sticks of damp-proofing fluid are inserted into pre-drilled holes. The ice sticks then melt gradually and the damp-proofing fluid spreads gradually across the brickwork and provides and effective damp-proof barrier. The only drawback is that it can be a time consuming process as after the first set of sticks has melted the process has to be repeated two or three times in order to form an effective damp-proof course but according to I'Anson & Hoff the correct installation of a pressure-injected damp-proof course would also be time consuming and the Freezteq damp-proofing system is acknowledged by most scientists in the remedial treatments industry as being the most effective form of retro-fit damp-proofing available today.

Transfusion damp-proofing method in use.
Bottles are filled with a siliconate damp-proofing fluid which is transfused into the capillaries of the brickwork, lining them with a hydrophobic layer which reverses capillary action and prevents moisture from rising. Because of the slow rate of saturation of the brickwork any voids or fissure are completely filled avoiding ‘viscous fingering’ which affects pressure injected damp-proof courses.
Gravity feeding allows the fluid time to penetrate fully into the pore structure of mortar, stone and brick, and is a more appropriate treatment for walls of hard stone set in soft lime mortars



Diffusion process
The Freezteq frozen damp-proof course works on a similar principle but frozen damp-proofing sticks are inserted into the brickwork which saturates the whole cross-section of the wall forming an effective damp-proof barrier

There is also another transfusion type damp-proofing system marketed by Koster Waterproofing which involves the drilling of holes and then injecting a damp-proofing resin which as well as being hydrophobic ( i.e water repellent ) is also a pore blocker and has proven to be very effective in preventing rising damp. However it can be time consuming as the injection/ diffusion process can take up to 48 hours and is more complicated than any other injected damp-proofing system and the whole process involves using resin cartridges, suction angle units and capillary tubes for each drilled hole but the manufacturers are very confident about it’s effectiveness in controlling rising damp. For further information contact Koster Aquatechnic in Dumfries on 01387 270252 or 

Believed to be used as long ago as the 1930s when the Knapen tube system was used at the Palace of Versailles and later patented by Royal Doulton after they found that their ceramic tubes appeared to attract and absorb moisture. These tubes were heavily marketed in the 1960’s and 70’s but fell out of favour with the public with the advent of chemical damp-proofing which could be done at roughly half the cost. Until recently this form of damp-proofing was only undertaken by one company in the UK (Hydrotek Wallguard) but their website does not give a comprehensive explanation of how this damp-proofing system works. There is now another company also offering this form of damp-proofing called Damp Solutions but again their website does not give any satisfactory explanation about how the tubes work, they just state the tubes work by ‘soaking up water from the surrounding brickwork and mortar course’.
Originally known as Knapen Tubes then Doulton Wallguard this method uses porous ceramic tubes which are fitted into walls at a slight angle to allow water/damp run off. The manufacturers state that ceramic material of the tubes has good suction properties and draws water from wall and into damp brickwork and into the inner part of the tube and this moisture then evaporates from the inner surfaces into the tube as this moisture laden air is relatively dense and gravitates to the base of the tubes and is vented externally which induces a natural ventilation process which encourages further drying.
There is no independent scientific evidence to show that this form of damp-proofing reduces rising damp but there does seem to be some evaporative effect just above ground level which can lead to a slight reduction in rising damp internally and allow re-decoration without the need for re-plastering.
To work properly the tubes must discharge externally so they are only useful on external walls of houses, if they were used on internal walls the moisture would be release internally which would increase humidity levels and possibly cause condensation dampness and also induced rising damp.
When properly installed the porous tube damp-proofing system can greatly increase the rate of evaporation from walls affected by damp but the tubes only cause drying in a localized area (a zone of evaporation) around each tube and unless the tubes are close enough together then there is the possibility that there are still paths for rising dampness to occur between the tubes.
Critics of the Wallguard/Knapen/Doulton damp-proofing systems say that the tubes become blocked with salts which reduce the evaporative effect but the fact that these hygroscopic salts are drawn into the tubes show that they are working and these can be removed very easily with compressed air.
A more elaborate system has been developed by Schrijver Damp Control ,Holland Damp Proofing and more recently Dr Damp all of which are designed to induce air-flow, condensation and moisture removal but they seem to be dependent on local wind and weather conditions, i.e. it depends on which way the wind blows . Research by the Independent Dutch Laboratory, TNO (Organisation for Applied Scientific Research) states that the performance of these damp-proofing tubes is governed by external environmental factors such as wind speed, wind direction, temperature and relative humidity and neither the Wallguard, Schrijver or Holland/Dr Damp systems of rising damp control have been awarded with a British Board of Agrément Certificate (BBA).
These much maligned damp-proofing systems do have some evaporative effect and will help walls dry out but so would the drilling of any 50mm diameter holes at the base of damp walls and if you are considering using this form of damp-proofing then please take a moment to look at the photos below to see how your property would be irreversibly disfigured at a cost of several thousand pounds when the same affect could be achieved at a fraction of the cost by installing extra air bricks or refurbishment weep vents.
The picture on the left shows a semi-detached house in Malvern, Worcestershire, the row of inserts at the base of the wall are intended to stop rising damp but this treatment was probably not needed as the house was built around 1930 and will have a functioning physical damp-proof course at the base of all the ground floor walls. The row of tubes on the first floor were probably to control condensation dampness but this could have been achieved easier and cheaper by the installation of two or three passive dehumidifiers. The row of inserts on the ground floor are about 300mm above the base of the front door and therefore even if this Dutch damp-proofing system is effective then rising dampness will still be affecting the wall up to the height of the vents which will result in dampness in plaster and also possible decay in skirting and other timbers abutting the ‘damp’ wall.
The photograph on the right is a terraced house in Sandycombe Road, Kew, Richmond TW9 3SU with the damp-proofing works being carried out at first floor level. Is this to stop rising damp or condensation dampness?


Electro Osmosis as a form of damp-proofing is a system first discovered in approx 1800 by the physicist Reuss in an experiment which showed that water could be forced to flow through porous clay diaphragms when an external electric field was applied. Flow is initiated by positive ions and is directed from the anode (positive anode) to the cathode (negative electrode) reversing the polarity of capillary action. In 1930, the Ernst brothers in Switzerland developed a system of applying electro-osmosis to drying out foundation walls. Three Hungarians, Miklos Lipscey, Imre Biczok and Zoltan Horvath, developed the system in Hungary, Paul Wieden did so in Austria and Dinu Moraru in Yugoslavia, and it was introduced in a patented system to Britain by W. J. Holmes of Rentokil and this system was used between 1962 and 1974 in over 55,000 houses before being superseded by the ever popular injected damp-proofing systems still used to this day.
However as the green lobby has grown there has been a resurgence in the use of electro-osmotic systems as a chemical free damp-proofing option and they generally consist of a titanium wire being installed at the base of the all walls and a small electrical charge applied. This system still involves a lot of internal disruption as the wire has to be fitted in mortar joints and all skirting boards will have to be removed to facilitate this. As with chemical damp-proofing plaster will have to be hacked off at least one metre high and then replaced with a waterproof render. This system may be chemical free but it is scientifically unproven and it is also quite expensive and the householder also has the hassle and mess of plaster being removed and the replacement of skirting etc after the work has been completed.
The Building Research Establishment has investigated electro-osmotic damp-proofing and it has some reservations about its effectiveness in controlling rising damp and this form of damp-proofing has never been awarded a British Board of Agrément Certificate (BBA).
The Building Research Establishment, in its Digest 245, confirms that a physical damp-proof course is the only completely sure method to cure rising damp but is very expensive, involving sawing out sections of a mortar bed and then inserting physical membrane.
Diamond tipped angel grinders are used to cut a section through the wall, of up to 1m in length. The dpc is then placed in the slot, bedded on mortar, with spacers inserted along the section to support the wall and compress the mortar. This wall is then repointed to create a finished job that is both neat and tidy, and – more importantly - effective. After the first section of wall is finished then the next metre of wall can be treated. It is a labour intensive and disruptive process but the work can be guaranteed for 50 years.
The lifespan of a physical damp course is far longer than any chemical damp-proofing and it creates a total barrier against rising damp.
Physical damp-proof course have been required to be inserted into all buildings constructed since approximately 1875. Initially this would have been a horizontal layer of slates overlapping to form a continuous barrier at the base of the wall, usually at the same height of the air bricks and in the 1930's this was replaced by bitumen which has now given way to the plastic rolls of damp-proof membrane that can be purchased from any builders merchants.
Slate damp course are still fairly effective in controlling dampness and often there is no need for any replacement damp-proof courses as most cases of 'rising damp' are in fact usually low-level penetrating dampness where water is sitting at the base of a wall or the original damp-proof course has been bridged, both of which create a 'moisture reservoir' allowing water to be drawn into the wall by capillary action and this then appears as rising damp internally.
Instead of installing a chemical damp-proof course it is usually easier and cheaper to tackle the problem externally by reducing ground levels or installing drainage channels to prevent bridging and repairing any drainage and guttering defects which may be causing ponding externally. Once these works have been carried out then the walls will dry out gradually and there is usually no need to remove plaster internally so as well as saving money by not having to have damp-proofing work done then all the mess and disruption of plastering and re-decorating internally is also avoided.
Even if there is any slight passage of moisture through the old damp course it rarely causes any problems internally as the rate of evaporation from the wall above the damp course is usually greater than the uptake of moisture below the damp course.
Inadequate sub-floor ventilation is often a cause of dampness in walls as this tends to cause a build-up of moisture in the floor void which can condense on the exposed masonry and timbers. Much of the condensate will be above the damp course and will then migrate upwards to appear as 'rising damp' internally. The easiest way to deal with this is to install extra air bricks at the base of the walls and ensure that there is an adequate through draught of air to remove moisture from the void, this will also help to reduce the moisture level of floor timbers and reduce the risk of decay and infestation.
The cost of a damp survey can be found here and can be arranged by phoning 0800 028 1903 or click the enquiry button to the left of the screen.